Includes Frank Siegel, Mary Siegfried, Sam Sillen, Marian Sills, Mary Silva, Horace Silver, Pat Silverstein, Modjeska Simkins, Calvin Simmons, Ira Simmons, Rev. Willie Sims, Rev. Tom Simpson, George F. Simpson (Steel Workers Organizing Committee), Dr. F. Vance Simonton, Abbott Simon, Prince Norodom Sihanouk, Ed Sinclair, Pat Singer, Burr Singer, Upton Sinclair, Lal Singh (Indian National Congress), and David Alfaro Siqueiros with Diego Rivera.